Preparation,Properties And Mechanism Research Of Starch Based Dispersants For Coal Water Slurry

The global energy crisis has existed all the time,and with the acceleration of industrial development in countries worldwide,the demand for energy is increasing.The major worldwide sources of energy are fossil fuels such as oil,coal and natural gas.Although human beings are seeking for new energy such as nuclear energy,solar energy,tidal energy and wind energy etc to solve energy crisis.The maturity and standardization of development and utilization technology of fossil fuels are more advanced and irreplaceable for a certain period of time.Fossil fuels are essential for human survival and development,occupying a large proportion in consumption of energy.China is a country rich in coal and poor in oil.Coal is very important for the national economic and social development,as the main energy source of our country.Coal is essential for the national sustainable development strategy.Low comprehensive utilization of coal resources at present is the main problem in our country.Scientific techniques are not widely applied.And at the same time,inefficient use of coals has caused serious environmental pollution.So the clean coal technology is imminent.The production of coal water slurry?CWS?is an application of clean coal technology.Improving efficiency and reducing emissions pollution must be considerated during the entire utilization process of coal resources.CWS is a kind of liquid coal fuel with high efficiency and less emissions.More and more attention has been paid to the preparation and application of CWS.The core of the technology is the preparation of highly effective environmental dispersants.The role of coal water slurry dispersant is to improve the density and the stability of slurry.At present,the types of dispersants are mainly lignin,naphthalene series,polycarboxylic acid series and humic acid series and so on.These dispersants have many problems,such as polluting the environment,high cost and poor adaptability.Some of them are based on petroleum feedstocks.Furthermore,these dispersants are mainly suitable for the high rank coal to prepare water slurry.As a result,the development of coal water slurry technology has been restricted.The worldwide attention to environmental pollution will inevitably lead researchers to pay attention to environmental friendly dispersants.Therefore,the research of coal water slurry dispersant is developing in the environmental friendly and biodegradable direction.Natural biological resources have gradually become an important direction in the study of dispersants for the preparition of coal water slurry.From the overall reserves of coal resources in China,the production of high rank coal is limited,while exist the low rank coal is widely existed.However,the research on dispersants for the preparation of the low rank coal is relatively few,resulting in the restriction of the further development and application of coal water slurry technology to more extensive use.The starch contains rich oxygen-containing functional groups,which have certain similarity with the structure characteristics of the low rank coals.Starch is rich in resources,and has a large amount of storage in nature.It can be biodegraded,with high safety and low price.The coal water slurry dispersant based on starch can be prepared by modifying the starch with the structural characteristics of the low rank coals.This type of dispersant is safe,environmentally friendly,and cheap.The rheological properties and stability of the prepared CWSs are better,which can meet the requirements of pulping and environmental protection.Different modified methods of corn starch have been studied and seven kinds of starch based dispersants were prepared.The synthesis process was optimized.The characterization of dispersants applied in Shenhua coal slurry was studied.Relationship between the molecular structures of CWS dispersants and dispersion and stability of coal water slurry was studied.And the mechanism was explored.It had a certain theoretical and practical value.This paper selected Shenhua coal as the object to study.Firstly,seven kinds of starch based coal water slurry dispersants were prepared through single and compound modification.With the hydroxyethyl starch,oxidized starch as raw materials,benzyl chloride as hydrophobic reagent,sixteen alkyl three methyl bromide as catalyst,water and isopropanol as solvents,we prepared two kinds of hydrophobically modified starch dispersing agent OBS and HBS.With the degradation and sulfonation process,the natural corn starch was modified to a hydrophilic starch dispersant SOS.With cationic starch as raw material,adding sodium styrene sulfonate?SSS?and acrylic acid?AA?,methyl allyl sulfonate?SMAS?and acrylic acid?AA?as grafting monomers,we prepared two kinds of amphoteric modified starch dispersing agent CSSAS and CSMAS.Two kinds of anionic modified starch HSS and SAS were prepared by polymerization reaction,adding hydroxyethyl acrylate?HEA?and styrene?ST?,sodium styrene sulfonate?SSS?and acrylic acid?AA?as grafting monomers.FT-IR,¹H NMR,GPC,TGA and DSC were used to characterize the structure and properties of the seven dispersants.The effects of dispersants on the dispersion and stability of slurry properties and rheological properties were studied to explore the relationship between the structure and dispersion.The results showed that these seven kinds of novel starch based modified dispersants had better dispersion and stability properties than the traditional NSF dispersant.Sulfonic groups,graft copolymerization of acrylic acid and sodium styrene sulfonate were conducive to the dispersion and stability of performance improvemen.They could effectively improve the performance.The initiator has a great influence on the graft copolymerization process.We found that NaHSO₃-K₂S₂O₈ was the optimum initiator.The introduction of a certain amount of cation in the dispersant structure could reduce the apparent viscosity of Shenhua coal water slurry,but it was not conducive to the stability of coal water slurry.The rheological properties of Shenhua coal water slurry prepared with seven kinds of starch based dispersants were studied.The apparent viscosity versus shear rate was determined,and the Power-law and Herschel-Bulkley models of coal water slurry were fitted.The results showed that CWSs prepared with the starch based disersants representing better pseudoplastic characteristics.The Power-law model of SOS coal water slurry showed high degree of coincidence,with the correlation coefficient R² 0.995;Herschel-Bulkley model of SAS CWS met the highest degree of fitting,the correlation coefficient R² was0.999,and the flow behavior index n was relatively low,showing more obvious characteristics of pseudoplastic fluid.The mechanism between starch based dispersants prepared with different modification methods and Shenhua coal was also expounded.The adsorption capacity and contact angle of the seven dispersants on Shenhua coal surface and the Zeta potential on the surface of composite coal particles were studied and compared.The results showed that these seven kinds of dispersants adsorbed on the surface of Shenhua coal were in line with the Langmuir isotherm equation.The anionic graft copolymerization of dispersed adsorption agent SAS could reach 2.97mg/g and the saturated adsorption amount of hydrophilic modified starch dispersant SOS could reach 2.61 mg/g.The saturated adsorption amounts of HBS and OBS were lower.These starch based dispersants could effectively improve the wettability of coal particles and reduce the contact angle.The SAS could reduce the contact angle to 62.56 degrees,while the SOS to 63.74 degrees.Seven kinds of starch based coal water slurry dispersants could effectively reduce the absolute value of Zeta potential on the surface of composite coal particles.The Zeta potential of the initial coal particle surface was-12.1mV,which showed that the charge of the surface of Shenhua coal particles was dominated by negative charges.With starch based dispersants,the absolute value of Zeta potentials of composite coal particles were increased in different degree.Dispersants could reduce the electronegativity and enhance the electrostatic repulsion between coal particles.It was conducive to the dispersion and stability of Shenhua coal in water.The structure characteristics of different modified starch prepared dispersant,combined with the structural characteristics of Shenhua coal were taken into comprehensive consideration.Meanwhile,the saturated adsorption capacity,the surface contact angle of Shenhua coal particles and Zeta potential changes were compared.The adsorption model of Shenhua coal and starch based dispersing agent and different structure is analyzed.Furthermore,The interaction mechanism between starch based dispersant and Shenhua coal is further clarified.